1. Field of the Invention
The present invention relates to prediction apparatus and method for a plasma processing apparatus, which predicts a state of process materials such as wafer processed in apparatuses for manufacturing semiconductors and the apparatus condition.
2. Description of the Related Art
Various processing apparatuses are used in the process of manufacturing semiconductors. For example, a processing apparatus such as plasma process apparatus is widely used in the process of depositing and etching objects to be processed such as semiconductor wafer and glass substrate. The plasma processing apparatus generates plasma using a process gas introduced in a hermetic process chamber. Thereafter, the apparatus carries out plasma processing with respect to objects to be processed, for example, the surface of semiconductor wafer. The forgoing plasma processing is repeated, and thereby, reactive products by plasma are generated, and thereafter, adhere to the inner wall of a process chamber. In addition, parts such as electrode provided in the process chamber are consumed. As a result, the apparatus condition subtly changes. The change of the apparatus condition gives influence to the etching shape of wafer. For this reason, the following parameters must be monitored in order to always carry out stable process. One of the parameters is the apparatus condition, that is, the thickness of parts provided in the process chamber. Another is the process result including process characteristic such as shape data of plasma-processed wafer.
For example, a test wafer is prepared, and thereafter, etching is periodically carried out with respect to the prepared test wafer. The condition of the processing apparatus is repeatedly determined based on the processing result (e.g., etched amount of the test wafer).
However, if the condition of the processing apparatus is repeatedly determined based on the test wafer, many test wafers must be prepared. In addition, there is a need of measuring the processing result every when many test wafers are processed using the processing apparatus. For this reason, the problem described below. That is, many processes and much time are taken to prepare the test wafers and to measure the processing result.
According to the technique (prediction method) disclosed in the following U.S. Patent Publication No. 2004-0007560, electrical data such as voltage and current of fundamental wave or integer multiple wave of a high frequency power source are agedly measured. Multiple regression analysis is made using the measurement data to prepare a predictive model, and thereafter, the thickness of a focus ring is predicted based on the predictive model.
The prediction method described above is excellent in prediction of the apparatus condition such as the thickness of the focus ring, however, the following case exists. Measurement data used when actually preparing the predictive model is not sufficient to carry out high accurate prediction, therefore, further improvement is required.
For example, in data used when actually preparing a model expression, there exists data contributing to a tendency of worsening a predicted value with respect to an observed value. In such a case, if data are all used without selecting the data used when preparing a model expression, correct prediction result is not conversely obtained.
The present invention has been made in view of the circumstances described above. Therefore, an object of the present invention is to provide prediction apparatus and method for a plasma process apparatus, which select data used for prediction based on multivariate analysis to improve prediction accuracy.